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15 page 
APPLICATION INFORMATION VIN GND EN FB TPS62270DRV VSEL L 2.2 H m SW C 10 F OUT m 0.9V 1.15V V 0.9V/1.15V upto400mA OUT V =2Vto6V IN C 4.7 F IN m OUTPUT FILTER DESIGN (INDUCTOR AND OUTPUT CAPACITOR) Inductor Selection DIL + Vout 1 * Vout Vin L ƒ (1) I Lmax + Ioutmax ) DIL 2 (2) www.ti.com ........................................................................................................................................... SLVS799C – NOVEMBER 2007 – REVISED JANUARY 2009 Figure 25. TPS62270DRV Application Circuit The TPS62270 is designed to operate with inductors in the range of 1.5 µH to 4.7µH and with output capacitors in the range of 4.7 µF to 22µF. The part is optimized for operation with a 2.2µH inductor and 10µF output capacitor. Larger or smaller inductor values can be used to optimize the performance of the device for specific operation conditions. For stable operation, the L and C values of the output filter may not fall below 1 µH effective inductance and 3.5 µF effective capacitance. The inductor value has a direct effect on the ripple current. The selected inductor has to be rated for its dc resistance and saturation current. The inductor ripple current ( ΔIL) decreases with higher inductance and increases with higher VI or VO. The inductor selection has also impact on the output voltage ripple in PFM mode. Higher inductor values will lead to lower output voltage ripple and higher PFM frequency, lower inductor values will lead to a higher output voltage ripple but lower PFM frequency. Equation 1 calculates the maximum inductor current under static load conditions. The saturation current of the inductor should be rated higher than the maximum inductor current as calculated with Equation 2. This is recommended because during heavy load transient the inductor current will rise above the calculated value. With: f = Switching Frequency (2.25 MHz typical) L = Inductor Value ΔIL = Peak to Peak inductor ripple current ILmax = Maximum Inductor current A more conservative approach is to select the inductor current rating just for the maximum switch current of the corresponding converter. Accepting larger values of ripple current allows the use of low inductance values, but results in higher output voltage ripple, greater core losses, and lower output current capability. The total losses of the coil have a strong impact on the efficiency of the DC/DC conversion and consist of both the losses in the dc resistance (R(DC)) and the following frequency-dependent components: • The losses in the core material (magnetic hysteresis loss, especially at high switching frequencies) • Additional losses in the conductor from the skin effect (current displacement at high frequencies) • Magnetic field losses of the neighboring windings (proximity effect) • Radiation losses Copyright © 2007–2009, Texas Instruments Incorporated 15 |
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